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Age Dating Fossils and Sediments

Age Dating Fossils and Sediments. Neal Immega. Direct Methods. Dendrochronology (tree rings) – 0 to 12,000 years (beginning of the Pleistocene) Greenland Ice Core – 0 to 800,000 years (middle of Pleistocene) Magnetic Reversals – 0 – 100 million years (beginning of the Cretaceous).

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Age Dating Fossils and Sediments

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  1. Age Dating Fossils and Sediments Neal Immega

  2. Direct Methods • Dendrochronology (tree rings) – 0 to 12,000 years (beginning of the Pleistocene) • Greenland Ice Core – 0 to 800,000 years (middle of Pleistocene) • Magnetic Reversals – 0 – 100 million years (beginning of the Cretaceous)

  3. Dating by tree rings • Excellent for dry sites that contain preserved wood like American Southwest. • Excellent way to calibrate C14 dating – max is 5%. • Has not been extended to fossil wood.

  4. Ice Cores • Record yearly data back 800,000 years. • Dust, pollen, volcanic ash, gas bubbles

  5. Magnetic Reversals – north is not always north • Cooling igneous rock picks up current magnetic field. • Settling sediments also align

  6. Sea Bottom – polarity stripes

  7. Sediments show magnetic reversals • Magnetic grains settle showing current magnetic field. • Lots of samples are needed in the section.

  8. Stored Energy Dating • Very popular with archeologists for pot dating • Thermo luminescence – heat to release energy • Optical Spin Luminescence – light will release energy • Electron spin resonance – magnetic field will measure stored energy

  9. Dating using Radioactivity • Potassium/Argon and Argon39/Argon40 • Uranium/Lead • Carbon 14 – special case • Fission track

  10. Radioactive Dating • Mass Spectrometry – accelerates ions in a magnetic field. • Different masses follow different paths.

  11. Radioactive parent element > normal daughter element

  12. K40/Ar40 and Ar39/Ar40 looks for argon trapped in the crystal

  13. Drawing by Dr. Bakker • Elapsed time since the crystal cooled.

  14. Drawing by Dr. Bakker

  15. Ar39/Ar40 Correct for weathering by progressive heating

  16. What do you date? • Date every ash layer and lava you can find. • Hopefully they will bracket the fossils you want to date – This is Olduvai gorge. basalt

  17. Drawing by Dr. Bakker

  18. Drawing by Dr. Bakker

  19. Drawing by Dr. Bakker

  20. Uranium/Lead dating - zircons

  21. Uranium fission tracks – etch crystal to show radiation damage

  22. Carbon 14 – continuous input

  23. DNA dating – accumulation of mutations • Estimate time of split between chimps and humans, Eve, dogs/wolves, …

  24. Dating Stratigraphy with Fossils

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